Surface illumination such as ceiling illumination has attracted considerable interest, for example to create a homogeneously lit space adjacent or below the surface in order to create comfortable working conditions, or to create light patterns on the illuminated surface, e.g. light stripes, in order to create an aesthetically interesting and invigorating illumination pattern on the surface.
Recently, solid state lighting (SSL) solutions, e.g. LED-based luminaires, have been proposed for such surface illumination, due to the superior lifetime, robustness and energy consumption characteristics of SSL devices compared to traditional light sources such as incandescent and fluorescent light sources. An example of such a SSL solution is given by US 2014/0362566 A1, which discloses a lighting system that includes a flexible light sheet and one or more sealed regions containing light-emitting elements, the sealed regions defined by seals between a top housing and bottom housing and/or the light sheet. Such a lighting system may be applied to curved surfaces and used as a ceiling luminaire but is less suitable for creating aesthetic luminous distributions such as light stripes along a target surface, e.g. a ceiling.
It is known to deploy lighting strips comprising a plurality of SSL elements in an elongation direction of the lighting strip in ceilings, e.g. in between the ceiling tiles of a modular ceiling. However, due to their positioning within the ceiling, such lighting strips provide direct illumination of the space below the ceiling, which can be perceived as rather bright and uncomfortable. It would be possible to suspend such lighting strips below the ceiling and direct the luminous output of the SSL elements towards the ceiling in order to create luminous pattern on the ceiling and indirectly illuminate the space below the ceiling through reflection and scattering effects. This arrangement has the disadvantage that the lighting strips when viewed from below are visible as a dark stripe along the ceiling, which is aesthetically undesirable.